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In my project i am connecting the LCD 16x2 same in Inductive load and it gets corrupt some times when valve switches ON/OFF , i put TVS in DC bias ,Snubber at AC side nothing worked out for me . though it is a product i cant use seperate supply lines for motors , AC valves and AC/DC converter .  Any robust solution , plz suggest .  -prag

[Reply #1 on:]

Decoupling capacitors in gay abandon around the  display and processor.

[Reply #2 on:]

I put Coils TVS diodes, Decaps of tantalum , this issue i am seeing associated with HD44870 only .   Lot of posts they discussed this issue but no hopeful solution yet ,

[Reply #3 on:]

Low value ceramic decoupling capacitors like 100nF for the high frequency stuff.

[Reply #4 on:]

Just a quick tought... try a 470 uF cap from 5V to LCD/Gnd, power device from mains source other than what the relay is controlling... It's possible that you are coupling a line transient through the PSU ground from the surge when the device turns on from the relay control. It is possible that your issue is something coupled into the  device through a lack of shielding... possible that you need an earthed (grounded) metal case as a shield. one last question... Where is the Arduinno powered... from the USB or a separate PSU into DC In?

Doc

[Reply #5 on:]

Thanks doc,   The board is powered from computer SMPS ,  I try putting high value caps in LCD area also .  In the system whenever Relay is getting switched off and ON it is happening .  some time SMPS also gets switched off ,all well grounded  , no earth leakage

[Reply #6 on:]

I have experienced similar issues with the lcd of my coffee machine controller when I flicked the mains switches. I found it helped to keep the LCD cables short and very tightly bundled together (read this somewhere but can't remember the technical background)....

[Reply #7 on:]

This i tried once i helped me , but not so much , LCD gets corrupted after some time later , i need rugged solution . 

[Reply #8 on:]

Since the Arduino drives the display use a 4K7 pull down on all the data and control leads. I think your issue is a floating port pin. In a quiet atmosphere it wouldn't make much different But a motor, particularly an inductive motor being switched on with a regular contactor is a very noisy thing. If the load hits at the right part of the cycle it is terrible... Right before the peak of the cycle and turning them off is no joke either as the energy stored in the motor's magnetic field has to go somewhere. 4K7 ohms will have minimal effect of the operation of your device and it's operation. you might welll be able to install them right on the back of the LCD itself.

Doc

[Reply #9 on:]

//My problem got sorted out after i made the PCB with display soldered and processor is very close to the display .//

No still corrupting some times ,even i put 4.7k ressitors on control and data lines ,still the same issue i am facing , plz suggest some rugged idea , i pullup all the unused pins too . 

[Reply #10 on:]

I connected 1N4148 diodes to all data and control lines with respect to ground .  the issue got  sorted out 100%  . also the EMI filter i connected between the critical valve which produces the EMI . Thanks DOC .